Happy to help. I got some more ideas.
I think a final character roster could look like this:
Haruka, Chihaya, Miki, Yukiho, Yayoi, Ritsuko, Azusa, Iori, Makoto, Ami, Mami, Hibiki, Takane, Ai, Eri, Ryo, Touma, Hokuto, Shouta, Uzuki, Rin, Mio, Ranko, Anzu/Kirari, Kaede, Mika, Minami, Mirai, Shizuka, Tsubasa, Serika, Nao, Kana, Shiho, Noriko, Teru, Kaoru, Tsubasa, Takeru, Ren, Pierre, Leon, Kuroi.
The roster is based on popularity, significance, or gameplay potential. Leon as a sub-boss, Kuroi as the final boss.
One small mechanic could be neutral combos by pressing A three times, although some characters will have a neutral infinite, kinda like Fox in Smash Bros. or E. Honda's Hundred Hand Slap, and if you let go, the infinitie will transition into a finisher. A good example could be Takeru having a multi-punch combo and go all JoJo with an ORAORAORAORAORA!
Pierre could be the oddball character with cartoonish abilities involving frogs.
This one seems a bit out there, but maybe have assist characters, like characters that are only used as assists, like Strikers in KOF. As in, you can summon NPCs to help you out in battle. Though that seems a bit much to implement.
... Sure, I'll bite. A long time ago, I started thinking to myself what a Cinderella Girls fighter would play like, probably 'cause I saw those fake screens and wished they were real. Now, there will never be a Cinderella Girls fighting game with all the characters in it, but eh.
A Cinderella Girls fighting game that plays similar to Ultimate Marvel vs Capcom 3 would be great! Maybe for combos, there can be like a combo breaker system like in Killer Instinct on Xbox One, where if you read the next attack of your opponent properly, you can break the combo, but if your opponent reads your breaker, they can counter that breaker and keep going. However, if one of these two screw up, they will not be able to do anything while being comboed or their combo will immediately end.
I can imagine for example Yukiho or Eri being characters based on counters/reversals, like Aoi from Virtua Fighter
I see that for Yukiho moreso than Eri, tbh. I expect Eri to be one huge reference to fighting games, given her nerdy attitude.